1. Field of the Invention
The present invention relates to an electrostatic discharge protection circuit, or ESD protection circuit. More particularly, the present invention relates to an electrostatic discharge protection circuit in a liquid crystal display (LCD).
2. Description of the Related Art
Electrostatic discharge is a phenomenon that electrostatic charge moves along the surface of a non-conductive material, which might damage circuit devices in an integrated circuit and other circuitry. For instance, when a human being is walking on a carpet, hundreds or even thousands of voltages of electrostatic potential might be detected under high relative humidity, whereas even tens of thousands of voltages might be detected under low relative humidity.
During a LCD fabrication, relevant machinery platforms and technicians under operation can carry electrostatic charges, thus when these charge bearers contact the LCD panels, an electrostatic discharge event might take place, and the momentary discharge might harm the LCD devices and permanently disable the circuitry.
In order to avoid device and circuitry damage caused by ESD, generally an ESD circuit is equipped with, are not in display on a LCD panel. The ESD circuit is usually formed along the periphery of a substrate (area not in display) under TFT fabrication. The detail description is as a first metal layer (M1) is defined on the substrate in the display are in order to form scanning lines and gates of active devices, gates of ESD circuit in the area not in display is as well defined on the substrate. Consequently, when a second metal layer (M2) is defined to form data lines and source/drain of the active devices in the area in display on the substrate, the source/drain of ESD circuit is as well defined in the area not in display on the substrate. Therefore, when the display panel suffers from ESD impact, the ESD scheme is triggered and the electrostatic charges are drained, thus internal circuitry and devices are free from direct discharge damage.
However, conventional ESD circuitry suffers from some issues, i.e. ESD circuit easily discharge at a point or a corner, or locations that bear high current density, so that devices in the vicinity are damaged easily. This is caused by conventional circuit layout, where corners and bending of ESD circuitry are involved, so that current density increases, and ESD occurs therein. In addition, ordinary ESD circuit is constructed with points in some locations in the layout, therefore chances of damage to vicinity devices is high. Provided the ESD circuitry are located at regions where the discharge event occur, the entire ESD circuit would be disabled.